Injectables and implants don’t boost cancer risk

Add the latest research finding to your counseling on progestin-only injectable and implant contraception: Results from a large U.S. study provide further evidence that these types of birth control do not raise a woman’s risk of breast cancer.1

Clinicians have long used combined findings from a Geneva-based World Health Organization multinational study and a study in New Zealand2 to counsel women that that use of depot medroxyprogesterone acetate (DMPA, Depo-Provera, Pfizer, New York City) does not affect the overall risk of breast cancer.

The new research offers reassurance to women who may have become concerned about cancer risks following information released from the estrogen/progestin arm of the Women’s Health Initiative (WHI), says Andrew Kaunitz, MD, professor and assistant chair in the obstetrics and gynecology department at the University of Florida Health Science Center/Jacksonville. The estrogen/progestin arm of the WHI trial was halted because the risk of breast cancer and heart disease from combined hormone replacement therapy outweighed its potential benefits.3

While 1 million to 2 million women in the U.S. currently use DMPA injections, implant contraception options have been lacking since the 2000 removal of the six-rod Norplant implant from U.S. pharmacy shelves. Wyeth Pharmaceuticals in Madison, NJ, suspended shipment of implants in August 2000 when concerns arose about efficacy of suspect lots. While the lots were found effective in July 2002, the manufacturer chose not to reintroduce the product in the United States.

With the possible introduction of the single-rod implant, Implanon (Organon, West Orange, NJ; now under review by the Food and Drug Administration), clinicians will want to keep the new research on hand to discuss with women if the implant is approved for use, Kaunitz comments.  

Review the results

The current research comes from the Women’s Contraceptive and Reproductive Experiences (CARE) Study, funded by the federal National Institute of Child Health and Human Development. The hypothesis in this paper arose from previous work suggesting that progestins might be related to breast cancer, says Brian Strom, MD, MPH, chairman of the department of biostatistics and epidemiology in the School of Medicine at the University of Pennsylvania in Philadelphia.4

The study looked at 4,575 randomly sampled women, ages 35-64, with primary invasive breast cancer diagnosed between 1994 and 1998, and compared them with 4,682 age and race-matched controls. Scientists then checked for previous DMPA and Norplant use.

Overall, 127 participants had used DMPA, and 12 had used Norplant. No significant increase or decrease in breast cancer risk was associated with use of either drug.

Previous findings from the Women’s CARE study indicated that oral contraceptives do not increase breast cancer risk.5 Compared to women who never had used the Pill, women who had used any type of oral contraceptive did not have a greater risk of developing breast cancer. When scientists analyzed different aspects of oral contraceptive exposure, such as ever, current, or former use; duration of use; age at first use; time since last use; and use by estrogen dose, they found little evidence that oral contraceptives increase breast cancer risk.

"Earlier findings from the Women’s CARE study provided reassurance that oral contraceptives do not increase the risk for breast cancer," Kaunitz says. "This new report indicates that progestin-only injectable and implantable contraceptives also are safe with respect to breast cancer risk."

References

1. Strom BL, Berlin JA, Weber AL, et al. Absence of an effect of injectable and implantable progestin-only contraceptives on subsequent risk of breast cancer. Contraception 2004; 69:353-360.

2. Skegg DC, Noonan EA, Paul C, et al. Depot medroxyprogesterone acetate and breast cancer. A pooled analysis of the World Health Organization and New Zealand studies. JAMA 1995; 273:799-804.

3. Writing Group for the Women’s Health Initiative Investigators. Risks and benefits of estrogen plus progestin in healthy postmenopausal women: Principal results from the Women’s Health Initiative randomized controlled trial. JAMA 2002; 288:321-333.

4. Weiss LK, Burkman RT, Cushing-Haugen KL, et al. Hormone replacement therapy regimens and breast cancer risk(1). Obstet Gynecol 2002; 100:1,148-1,158.

5. Marchbanks PA, McDonald JA, Wilson HG, et al. Oral contraceptives and the risk of breast cancer. N Engl J Med 2002; 346:2,025-2,032.